from greenlet import greenlet
import time

gr1 = greenlet(test1)
gr2 = greenlet(test2)

def test1():
  while True:
    print("----A----")
    gr2.switch()
    time.sleep(0.5)

def test2():
  while True:
    print("----B----")
    gr1.switch()
    time.sleep(0.5)

gr1.switch()

